The presence of coliform or other indicator bacteria is important evidence of food and water quality. The permitted amount of coliform bacteria found in drinking water or certain foods, such as dairy products, is regulated in many countries and/or municipalities. Coliforms include bacteria originating from nature, such as those found in soil. The coliform bacteria also include fecal coliforms, such as Escherichia coli. The presence of fecal coliforms in a sample is a primary indication of recent fecal contamination of the food or water, and of the possible presence of pathogenic organisms.
Methods for enumerating microbes in water samples can be found in, for example, the compendium “Standard Methods for the Examination of Water and Wastewater” (SMEWW), 21st Edition, which is a joint publication of the American Public Health Association, the American Water Works Association, and the Water Environment Federation. SMEWW describes a membrane filtration technique to obtain a direct count of microorganisms in water. Membrane filtration techniques are useful in monitoring the microbiological quality of samples from processes intended to produce drinking water, as well as samples from a variety of natural, unprocessed water sources.
Methods for enumerating microbes in food samples often vary according to the nature of the food and the types of organisms that are likely to be found in the samples. Several compendia of methods for testing food samples include “Standard Methods for the Examination of Dairy Products”, 27th Edition, published by The American Public Health Association, Washington, D.C., and the Bacteriological Analytical Manual (“BAM”), published by the U.S. Food and Drug Administration, Washington, D.C. Solid foods are usually suspended in aqueous media and mixed and/or pulverized to obtain a liquid homogenate of the food material, which can be used in methods of quantitative microbial analysis.
Each of the aforementioned methods typically requires a highly skilled technician to observe and interpret the test results. There is a need for a simple, accurate method for determining the number of microorganisms in a liquid sample.